The present invention relates to internal combustion engines, such as spark ignition and diesel engines. More particularly, the invention contemplates systems and methods for accommodating accelerated combustion expansion within the engine, such as occurs with minimum temperature auto-ignition.
In an internal combustion engine, a charge of fuel is ignited to cause rapid expansion of the resulting gases. This rapid expansion drives the pistons connected to the engine crankshaft. In the case of a spark ignition engine, the fuel is first introduced into the cylinder, compressed by action of the crank piston, and then ignited by a spark plug or other similar ignition source. In the case of a diesel engine, air is compressed by the piston to a particular pressure, fuel is injected into the high-pressure environment under circumstances in which the fuel will automatically ignite.
In spark and compression ignition engines, detonation, or engine "knock", may occur. Detonation is due to auto-ignition of end gas, or the part of the charge that has not yet been consumed by ignition flame front. This auto-ignition occurs when the unburned end gas is compressed by expansion of the burned part of the air/fuel charge. As the end gas is compressed, its temperature increases to a point at which the end gas automatically ignites. Rapid auto-ignition in a small volume causes detonation, leading to a rapid pressure spike within the engine cylinder. This detonation pressure spike usually generates intense vibrations in the cylinder walls that can cause damage to the cylinder head and to the face of the piston. Thus, the detonation of the secondary fuel and gases has been regarded as anathema in the design of internal combustion engines.
Numerous attempts have been made in engine design to prevent detonation or engine knock. For example, reducing the amount of fuel injected into the cylinder can eliminate the occurrence of detonation, with the resulting loss of power output from the cylinder. Varying the timing or rate of the fuel injection relative to the cylinder stroke also helps alleviate the ping problem.
Another approach to reducing knock has been the development of premium ethyl gasoline. The premium gasoline slows the burn cycle so that substantially all of the fuel burns without auto-ignition. The premium gasoline helps eliminate many engine knock problems with little sacrifice of output power. One downside of premium fuels is the added expense over lower octane or hybrid fuels.
All of these approaches go toward the elimination of detonation within the internal combustion engine cylinder. Many of these approaches reduce the engine power output, although some have a lesser effect than other approaches. There is a need for an internal combustion engine that can either avoid auto-ignition, or readily embrace auto-ignition without detonation. There is also a need for such an engine that avoids the problems of detonation while augmenting the power output of the engine over conventional engines.